6 Expressions

Expressions are the basic building blocks of awk patterns
and actions. An expression evaluates to a value that you can print, test,
or pass to a function. Additionally, an expression
can assign a new value to a variable or a field by using an assignment operator.

An expression can serve as a pattern or action statement on its own.
Most other kinds of
statements contain one or more expressions that specify the data on which to
operate. As in other languages, expressions in awk include
variables, array references, constants, and function calls, as well as
combinations of these with various operators.